A System of Logic, by John Stuart Mill

Chapter IV.

Of The Laws Of Mind.

§ 1. What the Mind is, as well as what Matter is, or any other question respecting Things in themselves, as
distinguished from their sensible manifestations, it would be foreign to the purposes of this treatise to consider.
Here, as throughout our inquiry, we shall keep clear of all speculations respecting the mind’s own nature, and shall
understand by the laws of mind those of mental Phenomena; of the various feelings or states of consciousness of
sentient beings. These, according to the classification we have uniformly followed, consist of Thoughts, Emotions,
Volitions, and Sensations; the last being as truly states of Mind as the three former. It is usual, indeed, to speak of
sensations as states of body, not of mind. But this is the common confusion, of giving one and the same name to a
phenomenon and to the approximate cause or conditions of the phenomenon. The immediate antecedent of a sensation is a
state of body, but the sensation itself is a state of mind. If the word Mind means any thing, it means that which
feels. Whatever opinion we hold respecting the fundamental identity or diversity of matter and mind, in any case the
distinction between mental and physical facts, between the internal and the external world, will always remain, as a
matter of classification; and in that classification, sensations, like all other feelings, must be ranked as mental
phenomena. The mechanism of their production, both in the body itself and in what is called outward nature, is all that
can with any propriety be classed as physical.

The phenomena of mind, then, are the various feelings of our nature, both those improperly called physical and those
peculiarly designated as mental; and by the laws of mind, I mean the laws according to which those feelings generate
one another.

§ 2. All states of mind are immediately caused either by other states of mind, or by states of body. When a state of
mind is produced by a state of mind, I call the law concerned in the case a law of Mind. When a state of mind is
produced directly by a state of body, the law is a law of Body, and belongs to physical science.

With regard to those states of mind which are called sensations, all are agreed that these have for their immediate
antecedents, states of body. Every sensation has for its proximate cause some affection of the portion of our frame
called the nervous system, whether this affection originates in the action of some external object, or in some
pathological condition of the nervous organization itself. The laws of this portion of our nature — the varieties of
our sensations, and the physical conditions on which they proximately depend — manifestly belong to the province of
Physiology.

Whether the remainder of our mental states are similarly dependent on physical conditions, is one of the vexatæ
questiones in the science of human nature. It is still disputed whether our thoughts, emotions, and volitions are
generated through the intervention of material mechanism; whether we have organs of thought and of emotion, in the same
sense in which we have organs of sensation. Many eminent physiologists hold the affirmative. These contend that a
thought (for example) is as much the result of nervous agency, as a sensation; that some particular state of our
nervous system, in particular of that central portion of it called the brain, invariably precedes, and is presupposed
by, every state of our consciousness. According to this theory, one state of mind is never really produced by another:
all are produced by states of body. When one thought seems to call up another by association, it is not really a
thought which recalls a thought; the association did not exist between the two thoughts, but between the two states of
the brain or nerves which preceded the thoughts: one of those states recalls the other, each being attended in its
passage by the particular state of consciousness which is consequent on it. On this theory the uniformities of
succession among states of mind would be mere derivative uniformities, resulting from the laws of succession of the
bodily states which cause them. There would be no original mental laws, no Laws of Mind in the sense in which I use the
term, at all; and mental science would be a mere branch, though the highest and most recondite branch, of the science
of physiology. M. Comte, accordingly, claims the scientific cognizance of moral and intellectual phenomena exclusively
for physiologists; and not only denies to Psychology, or Mental Philosophy properly so called, the character of a
science, but places it, in the chimerical nature of its objects and pretensions, almost on a par with astrology.

But, after all has been said which can be said, it remains incontestable that there exist uniformities of succession
among states of mind, and that these can be ascertained by observation and experiment. Further, that every mental state
has a nervous state for its immediate antecedent and proximate cause, though extremely probable, can not hitherto be
said to be proved, in the conclusive manner in which this can be proved of sensations; and even were it certain, yet
every one must admit that we are wholly ignorant of the characteristics of these nervous states; we know not, and at
present have no means of knowing, in what respect one of them differs from another; and our only mode of studying their
successions or co-existences must be by observing the successions and co-existences of the mental states, of which they
are supposed to be the generators or causes. The successions, therefore, which obtain among mental phenomena, do not
admit of being deduced from the physiological laws of our nervous organization; and all real knowledge of them must
continue, for a long time at least, if not always, to be sought in the direct study, by observation and experiment, of
the mental successions themselves. Since, therefore, the order of our mental phenomena must be studied in those
phenomena, and not inferred from the laws of any phenomena more general, there is a distinct and separate Science of
Mind.

The relations, indeed, of that science to the science of physiology must never be overlooked or undervalued. It must
by no means be forgotten that the laws of mind may be derivative laws resulting from laws of animal life, and that
their truth, therefore, may ultimately depend on physical conditions; and the influence of physiological states or
physiological changes in altering or counteracting the mental successions, is one of the most important departments of
psychological study. But, on the other hand, to reject the resource of psychological analysis, and construct the theory
of the mind solely on such data as physiology at present affords, seems to me as great an error in principle, and an
even more serious one in practice. Imperfect as is the science of mind, I do not scruple to affirm that it is in a
considerably more advanced state than the portion of physiology which corresponds to it; and to discard the former for
the latter appears, to me an infringement of the true canons of inductive philosophy, which must produce, and which
does produce, erroneous conclusions in some very important departments of the science of human nature.

§ 3. The subject, then, of Psychology is the uniformities of succession, the laws, whether ultimate or derivative,
according to which one mental state succeeds another; is caused by, or at least, is caused to follow, another. Of these
laws some are general, others more special. The following are examples of the most general laws:

First. Whenever any state of consciousness has once been excited in us, no matter by what cause, an inferior degree
of the same state of consciousness, a state of consciousness resembling the former, but inferior in intensity, is
capable of being reproduced in us, without the presence of any such cause as excited it at first. Thus, if we have once
seen or touched an object, we can afterward think of the object though it be absent from our sight or from our touch.
If we have been joyful or grieved at some event, we can think of or remember our past joy or grief, though no new event
of a happy or painful nature has taken place. When a poet has put together a mental picture of an imaginary object, a
Castle of Indolence, a Una, or a Hamlet, he can afterward think of the ideal object he has created, without any fresh
act of intellectual combination. This law is expressed by saying, in the language of Hume, that every mental
impression has its idea.

Secondly. These ideas, or secondary mental states, are excited by our impressions, or by other ideas, according to
certain laws which are called Laws of Association. Of these laws the first is, that similar ideas tend to excite one
another. The second is, that when two impressions have been frequently experienced (or even thought of) either
simultaneously or in immediate succession, then whenever one of these impressions, or the idea of it, recurs, it tends
to excite the idea of the other. The third law is, that greater intensity in either or both of the impressions is
equivalent, in rendering them excitable by one another, to a greater frequency of conjunction. These are the laws of
ideas, on which I shall not enlarge in this place, but refer the reader to works professedly psychological, in
particular to Mr. James Mill’s Analysis of the Phenomena of the Human Mind, where the principal laws of
association, along with many of their applications, are copiously exemplified, and with a masterly hand.270

These simple or elementary Laws of Mind have been ascertained by the ordinary methods of experimental inquiry; nor
could they have been ascertained in any other manner. But a certain number of elementary laws having thus been
obtained, it is a fair subject of scientific inquiry how far those laws can be made to go in explaining the actual
phenomena. It is obvious that complex laws of thought and feeling not only may, but must, be generated from these
simple laws. And it is to be remarked, that the case is not always one of Composition of Causes: the effect of
concurring causes is not always precisely the sum of the effects of those causes when separate, nor even always an
effect of the same kind with them. Reverting to the distinction which occupies so prominent a place in the theory of
induction, the laws of the phenomena of mind are sometimes analogous to mechanical, but sometimes also to chemical
laws. When many impressions or ideas are operating in the mind together, there sometimes takes place a process of a
similar kind to chemical combination. When impressions have been so often experienced in conjunction, that each of them
calls up readily and instantaneously the ideas of the whole group, those ideas sometimes melt and coalesce into one
another, and appear not several ideas, but one; in the same manner as, when the seven prismatic colors are presented to
the eye in rapid succession, the sensation produced is that of white. But as in this last case it is correct to say
that the seven colors when they rapidly follow one another generate white, but not that they actually
are white; so it appears to me that the Complex Idea, formed by the blending together of several simpler ones,
should, when it really appears simple (that is, when the separate elements are not consciously distinguishable in it),
be said to result from, or be generated by, the simple ideas, not to consist of them. Our
idea of an orange really consists of the simple ideas of a certain color, a certain form, a certain taste and
smell, etc., because we can, by interrogating our consciousness, perceive all these elements in the idea. But we can
not perceive, in so apparently simple a feeling as our perception of the shape of an object by the eye, all that
multitude of ideas derived from other senses, without which it is well ascertained that no such visual perception would
ever have had existence; nor, in our idea of Extension, can we discover those elementary ideas of resistance, derived
from our muscular frame, in which it has been conclusively shown that the idea originates. These, therefore, are cases
of mental chemistry; in which it is proper to say that the simple ideas generate, rather than that they compose, the
complex ones.

With respect to all the other constituents of the mind, its beliefs, its abstruser conceptions, its sentiments,
emotions, and volitions, there are some (among whom are Hartley and the author of the Analysis) who think that
the whole of these are generated from simple ideas of sensation, by a chemistry similar to that which we have just
exemplified. These philosophers have made out a great part of their case, but I am not satisfied that they have
established the whole of it. They have shown that there is such a thing as mental chemistry; that the heterogeneous
nature of a feeling A, considered in relation to B and C, is no conclusive argument against its being generated from B
and C. Having proved this, they proceed to show, that where A is found, B and C were, or may have been present, and
why, therefore, they ask, should not A have been generated from B and C? But even if this evidence were carried to the
highest degree of completeness which it admits of; if it were shown (which hitherto it has not, in all cases, been)
that certain groups of associated ideas not only might have been, but actually were, present whenever the more
recondite mental feeling was experienced; this would amount only to the Method of Agreement, and could not prove
causation until confirmed by the more conclusive evidence of the Method of Difference. If the question be whether
Belief is a mere case of close association of ideas, it would be necessary to examine experimentally if it be true that
any ideas whatever, provided they are associated with the required degree of closeness, give rise to belief. If the
inquiry be into the origin of moral feelings, the feeling for example of moral reprobation, it is necessary to compare
all the varieties of actions or states of mind which are ever morally disapproved, and see whether in all these cases
it can be shown, or reasonably surmised, that the action or state of mind had become connected by association, in the
disapproving mind, with some particular class of hateful or disgusting ideas; and the method employed is, thus far,
that of Agreement. But this is not enough. Supposing this proved, we must try further by the Method of Difference,
whether this particular kind of hateful or disgusting ideas, when it becomes associated with an action previously
indifferent, will render that action a subject of moral disapproval. If this question can be answered in the
affirmative, it is shown to be a law of the human mind, that an association of that particular description is the
generating cause of moral reprobation. That all this is the case has been rendered extremely probable, but the
experiments have not been tried with the degree of precision necessary for a complete and absolutely conclusive
induction.271

It is further to be remembered, that even if all which this theory of mental phenomena contends for could be proved,
we should not be the more enabled to resolve the laws of the more complex feelings into those of the simpler ones. The
generation of one class of mental phenomena from another, whenever it can be made out, is a highly interesting fact in
psychological chemistry; but it no more supersedes the necessity of an experimental study of the generated phenomenon,
than a knowledge of the properties of oxygen and sulphur enables us to deduce those of sulphuric acid without specific
observation and experiment. Whatever, therefore, may be the final issue of the attempt to account for the origin of our
judgments, our desires, or our volitions, from simpler mental phenomena, it is not the less imperative to ascertain the
sequences of the complex phenomena themselves, by special study in conformity to the canons of Induction. Thus, in
respect to Belief, psychologists will always have to inquire what beliefs we have by direct consciousness, and
according to what laws one belief produces another; what are the laws in virtue of which one thing is recognized by the
mind, either rightly or erroneously, as evidence of another thing. In regard to Desire, they will have to examine what
objects we desire naturally, and by what causes we are made to desire things originally indifferent, or even
disagreeable to us; and so forth. It may be remarked that the general laws of association prevail among these more
intricate states of mind, in the same manner as among the simpler ones. A desire, an emotion, an idea of the higher
order of abstraction, even our judgments and volitions, when they have become habitual, are called up by association,
according to precisely the same laws as our simple ideas.

§ 4. In the course of these inquiries, it will be natural and necessary to examine how far the production of one
state of mind by another is influenced by any assignable state of body. The commonest observation shows that different
minds are susceptible in very different degrees to the action of the same psychological causes. The idea, for example,
of a given desirable object will excite in different minds very different degrees of intensity of desire. The same
subject of meditation, presented to different minds, will excite in them very unequal degrees of intellectual action.
These differences of mental susceptibility in different individuals may be, first, original and ultimate facts; or,
secondly, they may be consequences of the previous mental history of those individuals; or, thirdly and lastly, they
may depend on varieties of physical organization. That the previous mental history of the individuals must have some
share in producing or in modifying the whole of their mental character, is an inevitable consequence of the laws of
mind; but that differences of bodily structure also co-operate, is the opinion of all physiologists, confirmed by
common experience. It is to be regretted that hitherto this experience, being accepted in the gross, without due
analysis, has been made the groundwork of empirical generalizations most detrimental to the progress of real
knowledge.

It is certain that the natural differences which really exist in the mental predispositions or susceptibilities of
different persons are often not unconnected with diversities in their organic constitution. But it does not therefore
follow that these organic differences must in all cases influence the mental phenomena directly and immediately. They
often affect them through the medium of their psychological causes. For example, the idea of some particular pleasure
may excite in different persons, even independently of habit or education, very different strengths of desire, and this
may be the effect of their different degrees or kinds of nervous susceptibility; but these organic differences, we must
remember, will render the pleasurable sensation itself more intense in one of these persons than in the other; so that
the idea of the pleasure will also be an intenser feeling, and will, by the operation of mere mental laws, excite an
intenser desire, without its being necessary to suppose that the desire itself is directly influenced by the physical
peculiarity. As in this, so in many cases, such differences in the kind or in the intensity of the physical sensations
as must necessarily result from differences of bodily organization, will of themselves account for many differences not
only in the degree, but even in the kind, of the other mental phenomena. So true is this, that even different
qualities of mind, different types of mental character, will naturally be produced by mere differences of
intensity in the sensations generally; as is well pointed out in the able essay on Dr. Priestley, by Mr. Martineau,
mentioned in a former chapter:

“The sensations which form the elements of all knowledge are received either simultaneously or successively: when
several are received simultaneously, as the smell, the taste, the color, the form, etc., of a fruit, their association
together constitutes our idea of an object; when received successively, their association makes up the idea of
an event. Any thing, then, which favors the associations of synchronous ideas will tend to produce a knowledge
of objects, a perception of qualities; while any thing which favors association in the successive order, will tend to
produce a knowledge of events, of the order of occurrences, and of the connection of cause and effect: in other words,
in the one case a perceptive mind, with a discriminate feeling of the pleasurable and painful properties of things, a
sense of the grand and the beautiful will be the result: in the other, a mind attentive to the movements and phenomena,
a ratiocinative and philosophic intellect. Now it is an acknowledged principle, that all sensations experienced during
the presence of any vivid impression become strongly associated with it, and with each other; and does it not follow
that the synchronous feelings of a sensitive constitution (i.e., the one which has vivid impressions) will be
more intimately blended than in a differently formed mind? If this suggestion has any foundation in truth, it leads to
an inference not unimportant; that where nature has endowed an individual with great original susceptibility, he will
probably be distinguished by fondness for natural history, a relish for the beautiful and great, and moral enthusiasm;
where there is but a mediocrity of sensibility, a love of science, of abstract truth, with a deficiency of taste and of
fervor, is likely to be the result.”

We see from this example, that when the general laws of mind are more accurately known, and, above all, more
skillfully applied to the detailed explanation of mental peculiarities, they will account for many more of those
peculiarities than is ordinarily supposed. Unfortunately the reaction of the last and present generation against the
philosophy of the eighteenth century has produced a very general neglect of this great department of analytical
inquiry; of which, consequently, the recent progress has been by no means proportional to its early promise. The
majority of those who speculate on human nature prefer dogmatically to assume that the mental differences which they
perceive, or think they perceive, among human beings, are ultimate facts, incapable of being either explained or
altered, rather than take the trouble of fitting themselves, by the requisite processes of thought, for referring those
mental differences to the outward causes by which they are for the most part produced, and on the removal of which they
would cease to exist. The German school of metaphysical speculation, which has not yet lost its temporary predominance
in European thought, has had this among many other injurious influences; and at the opposite extreme of the
psychological scale, no writer, either of early or of recent date, is chargeable in a higher degree with this
aberration from the true scientific spirit, than M. Comte.

It is certain that, in human beings at least, differences in education and in outward circumstances are capable of
affording an adequate explanation of by far the greatest portion of character; and that the remainder may be in great
part accounted for by physical differences in the sensations produced in different individuals by the same external or
internal cause. There are, however, some mental facts which do not seem to admit of these modes of explanation. Such,
to take the strongest case, are the various instincts of animals, and the portion of human nature which corresponds to
those instincts. No mode has been suggested, even by way of hypothesis, in which these can receive any satisfactory, or
even plausible, explanation from psychological causes alone; and there is great reason to think that they have as
positive, and even as direct and immediate, a connection with physical conditions of the brain and nerves as any of our
mere sensations have. A supposition which (it is perhaps not superfluous to add) in no way conflicts with the
indisputable fact that these instincts may be modified to any extent, or entirely conquered, in human beings, and to no
inconsiderable extent even in some of the domesticated animals, by other mental influences, and by education.

Whether organic causes exercise a direct influence over any other classes of mental phenomena, is hitherto as far
from being ascertained as is the precise nature of the organic conditions even in the case of instincts. The
physiology, however, of the brain and nervous system is in a state of such rapid advance, and is continually bringing
forth such new and interesting results, that if there be really a connection between mental peculiarities and any
varieties cognizable by our senses in the structure of the cerebral and nervous apparatus, the nature of that
connection is now in a fair way of being found out. The latest discoveries in cerebral physiology appear to have proved
that any such connection which may exist is of a radically different character from that contended for by Gall and his
followers, and that, whatever may hereafter be found to be the true theory of the subject, phrenology at least is
untenable.

270 When this chapter was written, Professor Bain had not yet published even the first part (“The Senses
and the Intellect”) of his profound Treatise on the Mind. In this the laws of association have been more
comprehensively stated and more largely exemplified than by any previous writer; and the work, having been completed by
the publication of “The Emotions and the Will,” may now be referred to as incomparably the most complete analytical
exposition of the mental phenomena, on the basis of a legitimate Induction, which has yet been produced. More recently
still, Mr. Bain has joined with me in appending to a new edition of the “Analysis,” notes intended to bring up the
analytic science of Mind to its latest improvements.

Many striking applications of the laws of association to the explanation of complex mental phenomena are also to be
found in Mr. Herbert Spencer’s “Principles of Psychology.”

271 In the case of the moral sentiments the place of direct experiment is to a considerable extent
supplied by historical experience, and we are able to trace with a tolerable approach to certainty the particular
associations by which those sentiments are engendered. This has been attempted, so far as respects the sentiment of
justice, in a little work by the present author, entitled Utilitarianism.